Eye-stinging smoke and a deafening crackling noise rose Monday from a prairie fire near the International Crane Foundation.

With humidity levels at more than 60 percent, the excess smoke and crackling were expected — as was the fire. The foundation relies on regular controlled burns to keep invasive plant species at bay and promote a healthy ecosystem to rear its captive bred birds.

Workers concentrated their efforts on a 35-acre section of grassland near the organization’s headquarters north of Baraboo. Foundation research coordinator Anne Lacy said prairie restoration efforts have taken place at the site since the organization was founded.

Lacy said the group burns five sections of property on a three-to-five-year cycle to control plants that drown out native species. Some problem plant species include sweet clover, Queen Anne’s lace and black locust.

“(Since we don’t) use chemicals we’d have to go out and dig them out,” Lacy said. “The one plant that we would miss would put another 100 plants out there.”

The section burned Monday is near the organization’s whooping crane rearing facility. Lacy said the grassland surrounding it serves as an area where young whooping cranes can explore their natural habitat before they are fully fledged.

“We have paths that are mowed through and they are able to go through and meander and get their exercise and get native foods,” Lacy said. “They can learn how to be cranes better than in an enclosure.”

International Crane Foundation volunteer Joe Lacy helps burn a section of grassland Monday near the organization's headquarters north of Baraboo.

JAKE PRINSEN/News Republic

Foundation workers and volunteers started the fire downwind in a small corner of the prairie field. The fuel they use is a combination of gasoline and diesel fuel, which limits combustion.

From there, two teams edged along grassland boundary and established a wet line with back tanks filled with water. Other workers used a tool called a flopper to stamp out small fires along the break.

“Anything to the right of this black line, we’re keeping it from burning past,” said Joe Lacy, Anne Lacy’s brother who volunteers for prescribed fires at the foundation. “Sometimes something will creep past the line after you go by.”

As the fire grew and burned up thick patches of vegetation, loud crackling drowned out workers’ voices. The sound was due to the wet conditions, Anne Lacy explained.

“The crackling is really heavy fuel, but it has a lot of moisture in it,” she said.

International Crane Foundation intern Sam Lei helps burn a section of grassland Monday near the organization's headquarters north of Baraboo.

JAKE PRINSEN/News Republic

The right “prescription” for a prescribed burn is a combination of ideal weather conditions. Lacy said wind must be blowing persistently in a given direction and humidity levels should be medium to high. She added that temperature also becomes a factor for workers, who wear thick Nomex shirts and pants, which is a fire resident material commonly worn by firefighters.

Foundation intern Sam Lei has worked at the organization since March. After helping out with several controlled burns, he said he was surprised at how much different fire behaves than in Hollywood.

“It has a very scientific way of moving,” he said. “It’s also much hotter than I thought it would be.”